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Jan. 26, 2009
Antarctica is getting warmer, according to a new study co-authored by Drew Shindell, a research scientist with NASA's Goddard Institute for Space Studies, an affiliate of Columbia University's Earth Institute. Scientists have known that ice shelves collapsing on the continent's northerly peninsula were the result of rapid warming, however evidence on temperature change in the continent's interior have been unclear; some have believed it might actually be cooling. This new research, however, shows temperatures are rising throughout the continent, at about the same pace as the rest of the world, consistent with rising levels of greenhouse gases in the air. The study is the cover article in the Jan. 22 issue of the leading scientific journal Nature.
Image credit: NASA Goddard Space Flight Center / University of Washington / US Geological Survey
In its report last year, the Intergovernmental Panel on Climate Change said that six of the world's seven continents were getting hotter, but that Antarctica still needed more investigation. Skeptics of human-caused climate change have used the idea of Antarctic cooling to debunk global warming. But the researchers of this new study say with a high degree of certainty that over the past 50 years, the continent as a whole has warmed nearly as fast as the rest of the world—about 1°F (.5°) on average. The western part has warmed even more rapidly over the same period—nearly 1.6°F (.85°C). The West Antarctic ice sheet is particularly susceptible to warming because much of it lies at low elevation. The complete melting of West Antarctica alone—equal to the combined size of Alaska, Texas, California and Kansas—would raise global sea levels by an estimated three to five meters.
"We're almost certain that increases in greenhouse gases on other continents are contributing to this warming in Antarctica," said Shindell, who is also an adjunct associate research scientist at Columbia's Center for Climate Systems Research.
Incomplete weather records had led scientists to think that much of Antarctica was cooling. About 100 manned and unmanned Antarctic weather stations have been gathering temperature data since 1957, but most are on the coast or the peninsula that juts toward South America, leaving most of the vast, inaccessible interior uncovered. Since 1981, satellite-generated data measuring the amount of infrared light reflected by snow gave a fuller picture. By correlating the weather station data with the satellite data, the scientists were able to reconstruct temperatures over the whole continent for the last 50 years.
"While some areas have been cooling for a long time, the evidence shows the continent as a whole is getting warmer," said the study's lead author Eric Steig, a glaciologist and geochemist at the University of Washington.
Shindell's role in the study was to determine what might be causing the warming. By plugging observed sea ice changes into a climate model, Shindell reproduced the warming trend that Steig and his colleagues found, especially in West Antarctica. The researchers believe that the retreat of sea ice off West Antarctica may be the key to explaining the warming.
Much of the west Antarctic ice sheet is grounded below sea level, surrounded by huge floating ice shelves that are subject to ocean currents. The scientists speculate that stronger winds from the Pacific are bringing warm air to West Antarctica, and that the warmer air is preventing new sea ice from forming. The warm winds are causing temperatures to rise on West Antarctica, and, as the ice disappears, additional heat is released into the air.
"One study is never really the last word," said Shindell. "But I think it'll be much harder for [skeptics] to argue against global warming... Now it appears that Antarctica, like the other continents, is following the expected response to greenhouse gases."
In addition to Steig and Shindell, the study was coauthored by David Schneider of the National Center for Atmospheric Research; Scott Rutherford of Roger Williams University; Michael Mann of Pennsylvania State University; and Josefino Comiso of NASA.
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